This project will focus on the role of arthropod gut epithelium in the transmission of parasitic, bacterial and viral infections. Arthropods play pivotal roles in many infections that significantly impact the health and performance of people and animals. In the first section of this proposal, Dr. Ganta will focus on the regulation of bacterial gene expression by tick epithelial cells. The long-term goals of this study are to elucidate how Ehrlichia species that are transmitted by ticks circumvent host immune processes and use the information to devise control strategies against the tick-transmitted pathogens. These goals will be addresses in the following two Specific Aims: 1) Determine the phenotype and genotype orE. chaffeensis from infected ticks. 2) Determine antigens that block transmission of E. chaffeensis from tick to mammalian host. This project will be the first to assess the feasibility of developing a vaccine for blocking the E. chaffeensis transmission from ticks. In the second section of this proposal, Dr. Clem will focus on the role of apoptosis in insect midgut epithelium in defense against microbial pathogens. The long term goal of this project is to increase our understanding of arthropod defenses against microbes, and to use this information to disrupt the transmission of human and animal pathogens that are vectored by arthropods. The central hypothesis of this proposal is that apoptosis can play a role in defense against microbial infection in the insect midgut epithelium. This hypothesis will be tested under the following two Specific Aims: 1) Determine whether apoptosis is stimulated by viral infection in insect midgut epithelial cells; 2) Characterize the apoptotic pathways induced by virus infection in insect cells. The proposed project thus addresses two key aspects of pathogen-arthropod host interactions that are fundamental to the pathogen survival and transmission.